In the field of long-distance optical communication, as the transmission rate has increased, managing the dispersion characteristics of optical transmission fibers has become an important issue. Polarization-mode dispersion (PMD) is one dispersion factor, and is caused by a group delay between two orthogonal polarization modes.
In optical fibers used for regular optical communication, since the core diameter has a shape that deviates from an ideal circle due to external stresses such as heat, tension, and pressure, birefringence occurs inside the core, which causes PMD. Since PMD is one factor limiting the transmission capacity in high-speed optical communication, it has become increasingly necessary to manage PMD in recent years.